The present invention relates to a device for the optical measurement of dental objects with the use of topometric measurement procedures.
In medical technology, dental medicine or dental technology prosthetic parts such as e.g. tooth crowns are being produced to an increasing degree with the aid of computer-supported systems. For this purpose it is initially necessary to produce, as basis for fabrication, a three-dimensional data set of the patient""s condition and of the planned prosthetic work in a binary format, which is effected in that the modelled conditionxe2x80x94that is for example a plaster stump, model segments, or even a complete model, and the prosthetic work modelled in wax by the dental technician, are measured.
In the meantime, in the manufacture of so-called frameworks, in some cases modelling in wax no longer takes place, but instead the workpiece is constructed by a specially trained dental technician with a 3D CAD system. Here also it is necessary to generate from the initial condition binary data which can then be applied in the computer-supported processing.
For the three-dimensional measurement of objects both mechanical scanning and optical measuring processes and apparatus are employed. In the case of optical measurement systems a distinction is in turn made between scanning processes, which measure the object to be measured point for point, and projection systems, which on the basis of a plurality of overall images of the object determine its three-dimensional structure. In the projection processes, the object to be measured is illuminated with structured light patterns and the projected pattern imaged by an observation system arranged at an angle to the direction of illumination. In accordance with the laws of triangulation, the imaged light structures are then evaluated and processed. Thereby, the object can be illuminated or observed from various directions, whereby from the totality of the images the three-dimensional structure is then calculated. Further, the object to be measured is illuminated with a plurality of lighting patterns, with a certain arrangement, which are for example displaced in phase or have different structures, whereby the accuracy of the optical measurement is significantly increased.
A process of this: kind is known from the literature as a so-called phase shift process and is described in detail in U.S. Pat. No. 4,641,972. A further development of this process is disclosed in DE 195 43 347 A1. Thereby, the projection grids employed for the generation of the different lighting structures are arranged on a common carriers with a pre-defined phase relationship, the carrier being pushed into the projection beam in the correct phase. Due to this special arrangement of the projection grids, the structure of the object to be measured can be determined with a very high accuracy.
Further there is known from DE 198 38 238 A1 a device for the computer controlled manufacture of dentures, in which the model of an upper or lower jaw to be measured is mounted on a wedge-shaped object receptacle and is rotated during the measurement.
All previously known optical measurement systems are of relatively complex structure, are mechanically sensitive 35 and for a dental technician can be operated only with difficulty. Thus, there is a need for an optical 3D measurement system which can be readily operated by persons involved in dental medicine and which can measure individual dental parts of any geometry.